.\" $OpenBSD: EVP_CIPHER_CTX_get_cipher_data.3,v 1.3 2023/08/26 15:12:04 schwarze Exp $
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.Dd $Mdocdate: August 26 2023 $
.Dt EVP_CIPHER_CTX_GET_CIPHER_DATA 3
.Os
.Sh NAME
.Nm EVP_CIPHER_CTX_get_cipher_data ,
.Nm EVP_CIPHER_CTX_set_cipher_data ,
.Nm EVP_CIPHER_CTX_buf_noconst
.Nd inspect and modify EVP_CIPHER_CTX objects
.Sh SYNOPSIS
.In openssl/evp.h
.Ft void *
.Fo EVP_CIPHER_CTX_get_cipher_data
.Fa "const EVP_CIPHER_CTX *ctx"
.Fc
.Ft void *
.Fo EVP_CIPHER_CTX_set_cipher_data
.Fa "EVP_CIPHER_CTX *ctx"
.Fa "void *cipher_data"
.Fc
.Ft unsigned char *
.Fo EVP_CIPHER_CTX_buf_noconst
.Fa "EVP_CIPHER_CTX *ctx"
.Fc
.Sh DESCRIPTION
.Fn EVP_CIPHER_CTX_get_cipher_data
returns a pointer to the cipher data of
.Fa ctx .
The format and content of this data is specific to the algorithm
and to the particular implementation of the cipher.
For example, this data can be used by engines
to store engine specific information.
The data is automatically allocated and freed by OpenSSL, so
applications and engines should not normally free this directly (but see
below).
.Pp
.Fn EVP_CIPHER_CTX_set_cipher_data
allows an application or engine to replace the existing cipher data
with new data, transferring ownership of
.Fa cipher_data
to the
.Fa ctx
object.
A pointer to any existing cipher data is returned from this function.
If the old data is no longer required,
it should be freed through a call to
.Xr free 3 .
.Pp
.Fn EVP_CIPHER_CTX_buf_noconst
provides engines and custom cipher implementations
with access to the internal buffer that
.Xr EVP_EncryptUpdate 3
copies input data into before encrypting it.
This function can for example be used
inside callback functions installed with
.Xr EVP_CIPHER_meth_set_do_cipher 3 .
.Sh RETURN VALUES
.Fn EVP_CIPHER_CTX_get_cipher_data
returns an internal pointer owned by
.Fa ctx .
.Pp
.Fn EVP_CIPHER_CTX_set_cipher_data
returns a pointer to the old cipher data of
.Fa ctx
and transfers ownership to the caller.
.Pp
.Fn EVP_CIPHER_CTX_buf_noconst
returns a pointer to an internal buffer owned by
.Fa ctx .
.Sh SEE ALSO
.Xr evp 3 ,
.Xr EVP_CIPHER_meth_new 3 ,
.Xr EVP_EncryptInit 3
.Sh HISTORY
.Fn EVP_CIPHER_CTX_get_cipher_data ,
.Fn EVP_CIPHER_CTX_set_cipher_data ,
and
.Fn EVP_CIPHER_CTX_buf_noconst
first appeared in OpenSSL 1.1.0 and have been available since
.Ox 7.1 .
